1. Field of the Invention
The invention relates to electrical switchboard apparatus having welded bus and more particularly to means for welding the main horizontal bus to the vertical riser bus forming a part of such switchboard apparatus.
2. Description of the Prior Art
An electrical distribution switchboard distributes the main incoming power among various site functions such as heating, lighting, and air conditioning. It typically consists of a number of vertical cabinet sections containing circuit breakers for switching and protecting the various load circuits. Three-phase electrical power enters a switchboard via cable or bus duct connected to a main bus which runs horizontally within the switchboard between the various sections. The main bus is connected to vertical, or riser, bus in each vertical cabinet section. Various circuit interrupters stacked vertically have their inputs connected to the vertical riser bus and their outputs connected to horizontal load size extensions which run toward the rear of the cabinet perpendicular to the main horizontal bus. Bus duct or cable is then attached to the load side extensions to permit the power to exit the switchboard and flow to the load (air conditioning, lights, motors, etc.).
The primary requirements for a switchboard are that it be safe and dependable, and that it exhibit low cost in construction, installation, and maintenance. Material cost and availability has influenced the choice of aluminum as the bus conductor material in some switchboard applications, since aluminum is readily available at an attractive cost and can be easily formed or extruded into any desired configuration. However, aluminum bus systems having joints formed with nuts and bolts (as is standard with copper bus systems) require periodic maintenance to assure satisfactory performance. This maintenance is costly and usually requires de-energization of the switchboard, causing great inconvenience to the users of the building being supplied by the switchboard.
Aluminum bus systems having welded connections eliminate the need for such maintenance. However, assembly of the switchboard can be much more costly and complicated due to the increase in complexity of welding precedures over bolting assembly methods in the confines of the switchboard cabinet framework. It is therefore desirable to provide a switchboard having a welded bus system suitable for a maximum of bench assembly operations prior to installation within the switchboard cabinet.
It has been found that savings can be achieved in the use of horizontal bus members having a plurality of spaced parallel-connected conductors rather than a single larger conductor having the same current carrying capacity. This is due primarily to greater cooling capability of parallel conductors, plus the increase in surface area which takes advantage of the "skin effect", whereby alternating current tends to flow at the surface of a conductor rather than its interior.
The use of such spaced parallel conductors means more complicated connections between the horizontal bus and the vertical riser bus. Prior art connections were often made by interleaving the incoming and outgoing horizontal bars at a horizontal-vertical junction, but this required an external jig fixture to properly position the bars during the welding operation. It is therefore desirable to provide a switchboard having a welded bus system which eliminates the need for an external fixture and which simplifies the welding operation required at a bus junction.